02 and respiratory failure Flashcards
what is type 1 respiratory failure?
- being short of oxygen with no impact of C02
what is type 2 respiratory failure?
- short of oxygen
- too much C02
what are the two mechanisms of type 1 respiratory failure?
- primary hypoxaemia in good lungs > increased Vt or increased RR (respiratory rate) > normal p02 and low pC02 > low p02 and normal pc02 = type 1
- primary hypoxaemia in bad lungs > low p02 and normal pC02
what are the mechanism of type 2 respiratory failure?
- same as type 1 > low p02 and normal pC02 > low p03 and high pC02
what produces acidosis?
- bad lungs > low p02 , high pC02 and normal HC03
or
low p02, very high pC02 and high HC03
why can it be dangerous to give too much 02 to people?
it can lead to increased C02 and acidosis > uncontrollable lung damage
what should be thought of when prescribing 02?
- oxygen is a drug
- only give is the risk/benefit ratio is in favour of it
- some people are very sensitive
- as p02 rises pC02 rises (acidosis, can be severe/ life threatening)
which patients are at risk of type 2 respiratory failure?
- some COPD patients (1 in5)
- kyphoscoliosis
- end stage CF
- morbid obesity
(nocturnal NIV - non invasive ventilation - is standard therapy for at risk groups )
what happens in V/Q mismatching when excess 02 is given?
- areas of poor ventilation have reactive vasoconstriction
- give excess 02 and that reactive vasoconstriction reverses
- perfusion becomes good but ventilation is still poor
Describe V and Q in a good lung.
in a normal lungs ventilation is good so localised oxygenation is good, there is vasodilation and goof perfusion V=Q
Describe V and Q in a bad lung?
ventilation is poor so localised oxygen is poor, there is hypoxic vasoconstriction and poor perfusion. both V and Q are small.
- blood is redirected to areas of good ventilation and away from the poor areas
what is the hypoxic drive theory?
- normal respiration is driven by C02 chemoreceptors
-chronic hypercarbia (high C02) leads to desensitisation of these receptors
-oxygen chemoreceptors then become the primary drive for respiration
(effects small compared to Haldane effect and V/Q mismatching)
what does V/Q mismatch tell us about the 02 that should be given?
patients with V/Q mismatch can be o2 sensitive
how is hypercarbia treated?
- conservative 02 management
- increase Vminute (increased Vt with NIV)
why is severe hypoxaemia bad?
- altered mental state, cyanosis, dyspnoea, tachypnoea, arrhythmias (tissue hypoxia)
- < 5.3 kPa = hyperventilation increases dramatically
- < 4.3 kPa = loss of consciousness
- <2.7 kPa = death
what is the equation for tissue hypoxaemia?
DO2 (delivery of 02 to tissues) = CO X [(Hb x Sa02) + 0.003 x Pa02]
Describe circulatory hypoxia
= hen oxygenated blood can’t get to the tissues
- global reduction = heart failure
- local reduction = obstruction of vessels, oedema, compression, compartments syndrome
what is anaemic hypoxia?
B12 and folate deficiencies cause anaemia
- koilonychias (spooning of nails) is a characteristic sign of this
- not very common in western world
- blood loss can cause iron deficiency
how does carbon monoxide poisoning occur?
- C0 binds irreversibly to Hb preventing 02 release and venous blood is therefore oxygenated
- cherry red venous blood is a sign and extremities can be bright red.
what is hypoxaemic hypoxia?
= low inspired 02 conc.
e.g at high altitudes or as a result of the use of anaesthetics
why might there be impaired diffusion?
- interstitial thickening (pulmonary fibrosis, lymphangitis, sarcoidosis)
- vascular dysfunction (pulmonary vasculitis, endothelial malignancy)
what is:
A) perfusion without ventilations
B) ventilation without perfusion
A - shunting
B -dead space
where is lung ventilation and perfusion good?
lung apex = good V poor Q
lung base = poor V good Q
which patients should receive unrestricted 02 use?
- cluster headaches, carbon monoxide poisoning, pneumothorax which hasn’t been drained and sickle cell crisis
Describe nasal cannulae.
- well tolerated
- low flow only
- uncontrolled Fi02
- dependant on nasal breathing
Describe variable performance masks.
- cheap and simple
- 5-15 l/min
- uncontrolled Fi02
- unable to cope with high flow requirements
Describe venture masks.
- fixed performance
- flows of up to 250 L/min
Describe a non-rebreathing mask.
-Up to 85 % FiO2
-Uncontrolled FiO2
-Flow limited to outflow of wall
-Beware large VT
-Indications for this mask are now very few
(CO poisoningPTX
Cluster headaches
Sickling crisis)